According to a study by France Webradios, the French National Association of Webradios :

On the streaming servers' side, Shoutcast ranks first (59%), followed by Icecast (29%), Windows Media (6%) and Darwin (6%).

The most widely used format is MP3 (40%), followed Windows Media (16%), Real (12 %), MP4 (8%), Ogg Vorbis (8%), Flash (8%), and AAC (8%). As far as bitrates are concerned, 128k (30 %) is the best compromise between broadcast quality and download bandwidth limits on the audience side. Then come 192k (17%), 56k (13%) and 24k (17%).

(translated from the press release)

That's rather good news for the Open Source codec people... but what about live video broadcasts (TV stations)?